1. Field of the Invention
The present invention relates to a system for measuring components of the velocity of a distribution of particulate matter along two axes. More specifically, the system measures a first axis projection and a second axis projection of a velocity of a distribution of particulate matter, such as a dust cloud structure moving with atmospheric wind.
2. Description of the Related Art
The high-resolution measurement of the components, or axial projections, of the velocity of wind in the lower atmosphere is needed for the detection of wind shear at airports, and for scientific investigations of turbulent transport in the atmospheric boundary layer. Radar-based wind profile systems, which are relatively large and expensive, are routinely used for these purposes but offer poor resolution. Sound-based xe2x80x9cSODARxe2x80x9d profilers also exist but have short ranges and poor reliabilities.
Some existing light detection and ranging (LIDAR) systems are used to measure wind velocity relying on the sweeping of a single laser beam through an area of interest. Such systems are disclosed in U.S. Pat. No. 5,724,125 to Ames, U.S. Pat. No. 5,796,471 to Wilkerson, and U.S. Pat. No. 5,872,621 to Wilkerson. Each of these LIDAR systems requires a discerning of Doppler shifts in return signals for wind velocity measurements and involves sophisticated, expensive equipment.
Alternative systems and methods have been discussed in literature by Kolev et. al. (xe2x80x9cLIDAR determinations of Winds by Aerosol Inhomogeneities: Motion Velocity in the Planetary Boundary Layerxe2x80x9d, Applied Optics, v. 27, n. 12, (June 1988) pp. 2524-2531), and by Parvanov et. al. (xe2x80x9cLIDAR Measurements of Wind Velocity Profiles in the Low Troposphere,xe2x80x9d presented at the 19th International Laser Radar Conference, Annapolis, Md., 1998). These publications detail xe2x80x9ctriple-beam soundingxe2x80x9d techniques in which three independent and spatially separated LIDAR devices generate separate signals. The signals are correlated at each altitude to determine the beam-to-beam transit time of particulate distribution structures and the transverse velocities of atmospheric winds carrying the structures. Such techniques suffer the disadvantage of requiring numerous separate LIDAR devices, each device requiring a light detection and data acquisition system.
It would be desirable to provide improved wind measurement systems and methods. The present invention addresses this problem and others in the manner described below.
The present invention relates to a system for measuring components of the velocity of a distribution of particulate matter along two axes that are transverse to the line of sight of the system. In an embodiment of the invention in which the distribution is dispersed in the atmosphere and wind velocity is to be measured, the line of sight can be essentially vertical. Such a system measures a first axis projection and a second axis projection of a velocity of a distribution of particulate matter, such as a dust cloud structure moving with wind. The system includes first and second light emitter arrays disposed along first and second axes, respectively, for illuminating the distribution with light, a detector for receiving light backscattered from the distribution, and a controller to activate the arrays, receive detector signals, and calculate the projections of the velocity of the distribution onto the first and second axes. The light emitters of each array can be positioned at irregular distances and provide the system with the capability of discerning the direction of movement of the distribution along the two axes.
In one embodiment of the invention, the light emitters are positioned along crossed axes to define a pair of crossed arrays and the irregular position distances of one array are different from the irregular position distances of the other array. The controller activates the arrays to illuminate the distribution in alternating fashion and correlates the storage of data for both arrays with a signal pulse sequence from a single detector. Each of the arrays can include a light source, such as a laser, optically coupled to a succession of beam splitters divergently aimed to illuminate the distribution.
A method is disclosed for measuring a first axis projection and a second axis projection of a velocity of a distribution of particulate matter. In one embodiment the method includes repeatedly and in alternating fashion generating pulses of light beams disposed along two axes, receiving backscattered light associated with each pulse using a detector, and determining the projections of the velocity of the distribution along the two axes by calculating a logarithm of a ratio of the Fourier transforms of detector signals.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.